
A useful schematic diagram of the LG effect is exhibited in Fig. REF . \(D_d\)  and \(D_{ds}\)  demonstrate the distance of the lens (L) from the observer (O) and the source (S) respectively. By assuming \(D_d, D_{ds}\gg r_0\) , we can obtain the deflection angle  [1]}
\(\hat{\alpha }(r_0)=2\int _{r_0}^{\infty }\frac{dr}{r\sqrt{\left(\frac{r}{r_0}\right)^2f_0-f}}-\pi .\) 
